Monday, August 20, 2012

New paper finds global cloudiness decreased over past 39 years

A new paper published in the Journal of Climate finds that from 1971 to 2009, "Global average trends of cloud cover suggest a small decline in total cloud cover, on the order of 0.4% per decade." Thus, over this 39 year period, global cloud cover decreased 1.56%. This decrease in cloud cover alone could account for all global warming since the 1970's. As Dr. Roy Spencer points out in his book,

"The most obvious way for warming to be caused naturally is for small, natural fluctuations in the circulation patterns of the atmosphere and ocean to result in a 1% or 2% decrease in global cloud cover. Clouds are the Earth’s sunshade, and if cloud cover changes for any reason, you have global warming — or global cooling."

Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195

Abstract

An archive of land-based, surface-observed cloud reports has been updated and now spans 39 years from 1971 through 2009. Cloud-type information at weather stations is available in individual reports or in long-term, seasonal, and monthly averages. A shift to a new data source and the automation of cloud reporting in some countries has reduced the number of available stations; however this dataset still represents most of the global land area.Global average trends of cloud cover suggest a small decline in total cloud cover, on the order of 0.4% per decade. Declining clouds in middle latitudes at high and middle levels appear responsible for this trend. An analysis of zonal cloud cover changes suggests poleward shifts of the jet streams in both hemispheres. The observed displacement agrees with other studies.
Changes seen in cloud types associated with the Indian monsoon are consistent with previous work suggesting that increased pollution (black carbon) may be affecting monsoonal precipitation, causing drought in North India. A similar analysis over northern China does not show an obvious aerosol connection.

Past reports claiming a shift from stratiform to cumuliform cloud types over Russia were apparently partially based on spurious data. When the faulty stations are removed, a tradeoff of stratiform and cumuliform cloud cover is still observed, but muted, over much of northern Eurasia.

August 20, 2012 at 11:54 pm“ Clouds, which cover about 60% of the Earth’s surface, are responsible for up to two thirds of the planetary albedo, which is about 30%. An albedo decrease of only 1%, bringing the Earth’s albedo from 30% to 29%, would cause an increase in the black-body radiative equilibrium temperature of about 1°C, a highly significant value, roughly equivalent to the direct radiative effect of a doubling of the atmospheric CO2 concentration.”